Linear Compressor With a Gas Spring

ABSTRACT

A refrigeration appliance, in particular at least one of a refrigerator, freezer and an air conditioning unit, includes a cooling chamber; a linear compressor having a piston housing; a compressor piston disposed within the piston housing and configured for reciprocatory motion along an axis within the piston housing; and buffer means for storing kinetic energy associated with the motion of the compressor piston, wherein the buffer means is configured to store the kinetic energy of the compressor piston in an interim manner by compression of a gaseous fluid during reciprocatory motion of the compressor piston.

The present invention relates to a refrigeration appliance, inparticular a refrigerator and/or freezer or an air conditioning unit,comprising a cooling chamber and a linear compressor, the linearcompressor having a piston housing and a compressor piston that can moveforward and backward along an axis therein as well as a buffer means forthe kinetic energy of the compressor piston moving forward and backward,a linear compressor for a refrigeration appliance and a method forcompressing a gas and a method for cooling goods.

With a linear compressor the compressor piston that can move forward andbackward along an axis between a first and second reversal point must besupported or guided in a direction perpendicular to said axis. Thekinetic energy of the compressor piston moving forward and backward mustalso be buffered at the reversal points, in other words at the pointswhere the direction of movement of the compressor piston is reversed, inorder to allow the direction of movement of the compressor piston to bereversed with as little loss as possible. By reversing the direction ofmovement, the compressor piston performs an oscillating, essentiallytranslatory, forward and backward movement in a compressor housing. Acompression process is executed with the aid of the forward and backwardmovement.

It is known that the movement energy of the compressor piston can bebuffered using one or more helical springs. The compressor piston mustalso be supported in a direction perpendicular to the direction ofmovement. Systems with an open structure, for example a seriallyarranged motor-pump arrangement, use a set of springs with one or morevery thin diaphragm springs or sets of diaphragm springs and one or morehelical springs or sets of helical springs to buffer the movement energyand to support the sides of the compressor piston in a directionperpendicular to the direction of movement. To ensure adequatestability, such springs or spring sets are made of metal. The diaphragmsprings are designed to be so thin and soft that the springs can absorbthe forces of the overall system produced perpendicular to theoscillation direction in the sum of their perpendicular rigidities withadequate reliability. To achieve appropriate longitudinal rigidityspring arrangements are known, in which diaphragm springs are backed upby one or more helical springs or sets of helical springs. Such springarrangements are however relatively complex in structure and aretherefore time-consuming to produce and assemble. If the spring force ofthe springs decreases over time or the spring forces of the individualsprings become unbalanced, friction can result between the compressorpiston and the piston housing, having an adverse effect on theefficiency of the linear compressor or the refrigeration unit andleading to increased energy consumption.

The object of the present invention is to specify a refrigerationappliance or a linear compressor for a refrigeration appliance, in whicha forward and backward movement of the compressor piston used isrealized both reliably and with energy savings in a simple manner duringcompression. The object is also to specify a method for compressing agas and a method for cooling goods, with which a compression and/orcooling process can be carried out with a high level of reliability in aparticularly energy-saving manner.

According to the invention this object is achieved by the refrigerationappliance and by the linear compressor for the refrigeration applianceand by the method for compressing a gas and by the method for coolinggoods, as set out in the independent claims. Further advantageousembodiments and developments, each of which can be applied individuallyor combined in any manner with one another, are the subject matter ofthe respectively dependent claims.

The inventive refrigeration appliance, in a particular a refrigeratorand/or freezer or an air conditioning unit, preferably an airconditioning unit for motor vehicles, comprises a cooling chamber and alinear compressor, the linear compressor having a piston housing and acompressor piston that can move forward and backward along an axistherein as well as a buffer means for the kinetic energy of thecompressor piston moving forward and backward, it being possible for thebuffer means to store the kinetic energy of the compressor piston in aninterim manner by compression of a gaseous fluid during the forward andbackward movement.

The linear compressor is used to compress a second fluid, in particulara refrigerant, in order to be able to produce refrigeration with adownstream evaporation stage. The second fluid is compressed by amovement of the compressor piston in the piston housing. The secondfluid can also be the gaseous fluid used for buffering.

Movement of the compressor piston essentially takes place along an axis.The compressor piston hereby oscillates between two reversal points, atwhich it briefly comes to rest, in order to change its direction ofmovement. At the reversal points a forward movement changes to abackward movement.

The buffer means is used to buffer the kinetic energy present in themovement of the compressor piston in the form of potential energy. Anoverall energy present in the movement of the compressor piston, whichis made up of the kinetic energy of the compressor piston and thepotential energy stored in the buffer means, remains essentiallyconstant. The buffer means in particular absorbs the movement energy ofthe compressor piston shortly before a reversal point and transfers itessentially totally back to the compressor piston after the movementdirection has been reversed. The aim of this is to convert themechanical energy brought by a drive unit almost totally into work atthe fluid to be compressed; in particular the drive unit should not takeon any slowing function for the compressor piston.

The gas to be compressed is located in particular in a sealed volume, onwhich a piston acts in a reducing manner. The pressure in the fluidincreases during compression. In particular during compression apressure is reached, which is greater, preferably 1 bar to 10 bargreater, in particular preferably 2 bar to 7 bar greater, than apressure that can be generated on a pressure side of the linearcompressor.

The buffer means can be used for example to prevent the compressorpiston striking a stop or a valve plate of the linear compressor in anuncontrolled manner, thereby reducing wear and saving energy for theoperation of the refrigeration appliance.

In contrast to known solutions, which provided a metal spring as thebuffer means, according to the invention the kinetic energy of thecompressor piston is stored by compressing a gaseous fluid. The buffermeans can be in the form of a gas pressure spring.

The buffer means absorbs preferably at least 90%, in particular at least95%, preferably at least 99%, of the kinetic energy present in themovement of the compressor piston before a reversal point. The buffermeans then transfers at least 88%, in particular at least 97%, of thisenergy back to the compressor piston, with the result that thecompressor piston, which has slowed down out of the forward movement andcome to rest at the reversal point, is again accelerated during itsbackward movement.

The gaseous fluid can be identical to or different from a second fluidcompressed by the linear compressor. The gaseous fluid can for examplebe a refrigerant compressed by the linear compressor. Essentiallyhowever any gas can be used for buffering. Air could be used for examplein a compressed air spring.

The means advantageously comprises a compression chamber formed by thepiston housing and the compressor piston and in particular being able tobe sealed during and/or due to the forward and backward movement of thecompressor piston. The compression chamber can be sealed by thecompressor piston itself but it can also be sealed with the aid ofvalves.

The compression chamber can be formed by a dead space in the pistonhousing. The dead space is bounded by walls of the compressor housingand a top face of the compressor piston. In this embodiment no valvesare required to bring about interim compression of the gaseous fluid inthe dead space, as the compressor piston compresses the gaseous fluid inthe dead space.

In an alternative embodiment the compression chamber has valves, whichare activated in phase, in other words opened or closed, during theforward and backward movement of the compressor piston.

The means advantageously has a valve, which closes before the movementdirection of the compressor piston is reversed and opens again after themovement direction of the compressor piston has been reversed. Thismeans that the valve opens and closes at least once per cycle.

In particular the valve closes during a forward movement and opensduring a backward movement immediately following the forward movement.

In one particular embodiment the valve closes during a forward movementwithin a segment of 50% of the piston travel of the forward and backwardmovement before a reversal point of the compressor piston, in particularwithin a segment of 20% of the piston travel before a reversal point ofthe compressor piston, in particular within 10% of the piston travelbefore the reversal point of the compressor piston. The compressorpiston is slowed down within the segment until it stops at a reversalpoint.

In a further specific embodiment of the invention the valve opens duringa backward movement within a segment of 50% of the piston travel of theforward and backward movement after a reversal point of the compressorpiston, in particular within a segment of 20% of the piston travel aftera reversal point of the compressor piston, in particular within 10% ofthe piston travel after the reversal point of the compressor piston. Thecompressor piston is accelerated back to its original speed within thissegment, the buffer means transferring the energy stored in it back tothe compressor piston.

Similarly during a forward or backward movement a top surface of thecompressor piston can extend into the dead space by a segment of atleast 5% of the piston travel of the forward and backward movement, inparticular by a segment of at least 10% of the piston travel, preferablyby a segment of at least 30% of the piston travel, in order to compressthe gaseous fluid enclosed by the inner chamber and the compressorpiston.

The compressor piston is advantageously guided in the piston housingwith the aid of a housing wall with openings and a gaseous fluid flowingthrough the openings, in particular a refrigerant. Such guide systemscan operate without oil. This guide system allows the compressor pistonto be supported in a radial direction, in other words in a directionperpendicular to the axis. The fluid flowing through the openings causesa gas cushion to be produced in front of the housing wall, by means ofwhich the compressor piston is supported in a contactless manner in thepiston housing.

A buffer means is advantageously provided at both reversal points of thecompressor piston, it being advantageously possible for the buffer meansto store the kinetic energy of the compressor piston in an interimmanner by compression of a gaseous fluid during the forward and backwardmovement.

Combined forms can also be used, in which the kinetic energy is storedat the one reversal point by compression of the gaseous fluid, while atthe other reversal point the kinetic energy is buffered with the aid ofa spring or a set of springs, in particular with the aid of a metalspring or a set of metal springs.

The buffer means can also be an elastic element, in particular a spring,preferably a diaphragm spring or a set of diaphragm springs, made of acomposite material. A composite material is a structural material madeup of two or more different materials, e.g. fibers, plastic, metal,ceramics. At least one component, for example fibers, is inlaid in thebase structure, known as a matrix. The intention here is to combine thedifferent advantages of the individual materials in the final materialand to eliminate their disadvantages. Carbon fiber reinforced plastics(CFK), glass fiber reinforced plastics (GfK), TiGr composite, in otherwords a compound of titanium, graphite and epoxy resin, as well ascertain polyaramides, in particular polyphenylene terephthalamide (knownunder the trade name Kevlar) and others can be used as the compositematerial.

Compression of the gaseous fluid allows the kinetic energy of thecompressor piston to be buffered reliably for the movement directionreversal, thereby allowing reliable and energy-saving operation of therefrigeration appliance.

The inventive linear compressor is particularly suitable and intendedfor the inventive refrigeration appliance and has a piston housing and acompressor piston that can move forward and backward along an axistherein as well as a buffer means for the kinetic energy of thecompressor piston moving forward and backward, it being possible for thebuffer means to store the kinetic energy of the compressor piston in aninterim manner by compression of a gaseous fluid during the forward andbackward movement.

The means can comprise a compression chamber, in particular a deadspace, formed by the piston housing and a top surface of the compressorpiston, which can in particular be sealed by the forward and backwardmovement. The means preferably has a valve, which closes before themovement direction of the compressor piston is reversed and opens againafter the movement direction of the compressor piston has been reversed.

The valve can close during a forward movement within a segment of 50% ofthe piston travel of the forward and backward movement before a reversalpoint of the compressor piston, in particular within a segment of 20% ofthe piston travel before a reversal point of the compressor piston, inparticular within 10% of the piston travel before the reversal point ofthe compressor piston.

The valve can also open during a backward movement within a segment of50% of the piston travel of the forward and backward movement after areversal point of the compressor piston, in particular within a segmentof 20% of the piston travel after a reversal point of the compressorpiston, in particular within 10% of the piston travel after the reversalpoint of the compressor piston.

A top face of the compressor piston can also by a segment of at least5%, in particular by at least 10%, preferably by at least

Similarly during a forward or backward movement a top surface of thecompressor piston can extend into a dead space by a segment of at least5% of the piston travel of the forward and backward movement, inparticular by a segment of at least 10% of the piston travel, preferablyby a segment of at least 30% of the piston travel, in order to compressthe gaseous fluid enclosed by the inner chamber and the compressorpiston.

The compressor piston can be guided in the piston housing with the aidof a housing wall with openings and a gaseous fluid flowing through theopenings, in particular a refrigerant.

In particular the linear compressor has a buffer means at both reversalpoints of the compressor piston.

All the features of the linear compressor described in relation to therefrigeration appliance can thus be applied to the inventive linearcompressor and advantageously utilized. This provides a linearcompressor, which is particularly robust and reliable and operates in anenergy-saving manner.

The inventive method for compressing a gas with the aid of arefrigeration appliance comprising a linear compressor, the linearcompressor having a piston housing and a compressor piston that can moveforward and backward along an axis therein provides for a majority ofthe kinetic energy of the compressor piston moving forward and backward,in particular up to more than 90%, preferably up to more than 95%, inparticular preferably essentially in its totality, to be buffered withthe aid of a gas cushion, to bring about a reversal of the movementdirection of the compressor piston moving forward and backward.

A gaseous fluid is advantageously compressed by the movement of thecompressor piston, with the result that the compressor piston is sloweddown and comes to rest. The energy stored in the compression is thenused again to accelerate the compressor piston in the counter direction,in other words in the backward direction, to the sum of the originalspeed so that the energy stored in the form of a potential energy isconverted back to kinetic energy. The movement direction can be reversedessentially without the aid of a drive unit, i.e. in a drive-freemanner.

The gas cushion can be produced by compressing the gaseous fluid. Thegaseous fluid is in particular a refrigerant for a refrigerationappliance. The gas cushion can however also be formed by compressinganother gas, in particular air.

The gas cushion is advantageously formed by a gaseous fluid compressedby means of the compressor piston itself. To this end the gas cushion isformed in that an inner chamber is enclosed and sealed by the pistonhousing and the compressor piston shortly before the movement directionof the compressor piston is reversed. After the movement direction hasbeen reversed, the inner chamber is opened again. The opening andclosing of this inner chamber takes place in phase with the forward andbackward movement of the compressor piston.

However the gas cushion can also be produced using a separate gaspressure spring.

For example the inner chamber can be sealed by the compressor pistonitself, if the inner chamber is embodied as dead space, and thecompressor piston compresses the enclosed gaseous fluid during itsmovement into the inner chamber. Compression causes the compressorpiston to slow down out of the forward movement and accelerate into abackward movement.

The inner chamber is advantageously sealed within a time interval of aquarter of the period length of the forward and backward movement, inparticular an eighth of the period length of the forward and backwardmovement, before the time of the movement direction reversal. Sealingthe inner chamber within this time interval causes the compressor pistonto be slowed down in this time interval.

The inner chamber is advantageously opened within a time interval of aquarter of the period length of the forward and backward movement, inparticular an eighth of the period length of the forward and backwardmovement, after the time of the movement direction reversal. Within thistime interval the compressor piston is accelerated back to its originalspeed that it had before the inner chamber was sealed.

The inventive method for cooling goods uses the inventive refrigerationappliance and/or the inventive linear compressor. Such use allows aparticularly reliable, energy-saving and fast cooling of goods.

Further advantageous details and specific embodiments are described inmore detail with reference to the drawing below, which is not intendedto restrict the invention but simply to illustrate it by way of examplesand in which:

FIG. 1 shows a schematic sectional view of an inventive linearcompressor;

FIG. 2 shows a schematic sectional view of an inventive refrigerationappliance; and

FIG. 3 shows a schematic sectional view of a further inventive linearcompressor.

FIG. 1 shows a sectional view of an inventive linear compressor 1 with apiston housing 1, in which a compressor piston 4 moves forward andbackward along an axis 3 between a first reversal point 8 of thecompressor piston 4 and a second reversal point 9 of the compressorpiston 4. The kinetic energy of the compressor piston 4 is stored in aninterim manner with the aid of a buffer means 6, in order to bring abouta reversal of the movement direction of the compressor piston 4 withlittle energy loss. The linear compressor 1 has a suction connection 14with a first valve 10 and a pressure connection 15 with a second valve11. The linear compressor 1 is used to compress a gaseous fluid 5. Whilethe pressure supplied at the pressure connection 15 is around 8 to 9bar, the pressure in the compression chamber 7 is somewhat higher duringcompression for buffering and is around 10 bar. The first valve 10 andsecond valve 11 are hereby activated with the aid of a valve plate 16 inphase with the forward and backward movement of the compressor piston 4,so that a gas compression cushion 12 is formed in an inner chamber 13 infront of the compressor piston 4, in which the gaseous fluid 5 iscompressed. Compressing the gaseous fluid 5 in the inner chamber 13slows down the movement of the compressor piston 4, its kinetic energybeing converted essentially totally to the potential energy inherent inthe gas compression cushion 12. The compressor piston 4 is supportedwith the aid of a housing wall 23 with openings 22, in that some of thefluid 5 flows through the openings 22, thereby forming a gas pressurebearing, which guides the compressor piston 4 in a contactless manner infront of the housing wall 23. The fluid 5 required for this is suppliedcontinuously via a feeder 17 and forms a gas bearing cushion 18 betweenthe compressor piston 4 and the housing wall 23. The compressor piston 4is driven with the aid of a drive unit 25 by way of a piston rod 19. Thehousing wall 23 embodied as a sleeve is sealed with the aid of an O-ring21. A spring 26 is used to assist the storage of the kinetic energy bythe buffer means 6, said spring 26 being carbon fiber reinforced andtherefore able to absorb lateral forces of the piston rod 19, i.e.forces directed in a direction perpendicular to the axis 3.

The compressor piston 4 moves between the reversal points 8 and 9 with apiston travel H. The compressor piston 4 is slowed down over a segment Sby closing the valves 10, 11 and forming a gas compression cushion 12and then accelerated again after reversal of the movement direction. Thehousing wall 23 together with the compressor piston 4 forms acompression chamber 7, when the valves 10, 11 are closed, in whichcompression chamber 7 the gaseous fluid 5 can be compressed.

FIG. 2 shows a sectional view of the inventive refrigeration appliance20 with the linear compressor 1 and a cooling chamber 27, in which goods24, in particular food, can be cooled swiftly, reliably and in anenergy-saving manner.

FIG. 3 shows a sectional view of a further embodiment of the inventivelinear compressor 1, the inner chamber 13 being embodied as dead space28. Whenever the compressor piston enters this dead space 28, thegaseous fluid 7 is compressed to form a gas cushion 12. The compressorpiston 4 itself seals the dead space 28. It is advantageous here that itis impossible for the compressor piston 4 to strike the valve plate 16,even if the valves 10, 11 temporarily fail to close correctly, as thedead space 28 does not require any further valves closing in phase. Thevalves 10, 11 can only be used to open and/or close the suctionconnection 14 and/or the pressure connection 15 at a thermodynamicallyfavorable time.

The invention relates to a refrigeration appliance 20, in particular arefrigerator and/or freezer or an air conditioning unit, comprising acooling chamber 27 and a linear compressor 1, the linear compressor 1having a piston housing 2 and a compressor piston 4 that can moveforward and backward along an axis 3 therein as well as a buffer means 6for the kinetic energy of the compressor piston 4 moving forward andbackward, it being possible for the buffer means 6 to store the kineticenergy of the compressor piston 4 in an interim manner by compression ofa gaseous fluid during the forward and backward movement; a linearcompressor with such a buffer means 6 and a method for compressing agaseous fluid 5 with the aid of said refrigeration appliance 20 and amethod for cooling goods. The invention is characterized in that simpleand efficient buffering of the kinetic energy of the moving parts in thelinear compressor 1 is possible with the aid of gas compression,allowing reliable and energy-saving operation during compression and/orduring cooling.

LIST OF REFERENCE CHARACTERS

-   1 Linear compressor-   2 Piston housing-   3 Axis-   4 Compressor piston-   5 Fluid-   6 Buffer means for the kinetic energy of the compressor piston 4    moving forward and backward-   7 Compression chamber-   8 First reversal point of compressor piston 4-   9 Second reversal point of compressor piston 4-   10 First valve-   11 Second valve-   12 Gas compression cushion-   13 Inner chamber-   14 Suction connection-   15 Pressure connection-   16 Valve plate-   17 Feeder-   18 Gas bearing cushion-   19 Piston rod-   20 Refrigeration appliance-   21 O-ring-   22 Openings-   23 Housing wall-   24 Goods-   25 Drive unit-   26 Spring-   27 Cooling chamber-   28 Dead space-   Top surface-   H Piston travel-   S Segment within piston travel H

1-14. (canceled)
 15. A refrigeration appliance, in particular at leastone of a refrigerator, freezer and an air conditioning unit, comprisinga cooling chamber; a linear compressor having a piston housing; acompressor piston disposed within the piston housing and configured forreciprocatory motion along an axis within the piston housing; and buffermeans for storing kinetic energy associated with the motion of thecompressor piston, wherein the buffer means is configured to store thekinetic energy of the compressor piston in an interim manner bycompression of a gaseous fluid during reciprocatory motion of thecompressor piston.
 16. The refrigeration appliance according to claim 15wherein the buffer means includes a compression chamber formed by thepiston housing and the compressor piston configured for being sealedduring compressor piston movement.
 17. The refrigeration applianceaccording to claim 15 wherein the buffer means includes a valveconfigured for closing before the compressor piston reverses directionand opening after the compressor piston reverses direction.
 18. Therefrigeration appliance according to claim 17 wherein the valve closesduring a forward compressor piston movement within a segment of 50% ofthe piston travel of the reciprocatory movement before a reversal pointof the compressor piston, in particular within a segment of 20% of thepiston travel before a reversal point of the compressor piston, inparticular within 10% of the piston travel before the reversal point ofthe compressor piston.
 19. The refrigeration appliance according toclaim 17 wherein the valve is configured for opening during a backwardmovement within a segment of 50% of the piston travel of the forward andbackward movement after a compressor piston reversal point, inparticular within a segment of 20% of the piston travel after acompressor piston reversal point, in particular within 10% of the pistontravel after a compressor piston reversal point.
 20. The refrigerationappliance according to claim 15 and further comprising a plurality ofopenings formed in the housing wall, wherein the compressor piston isguided in the piston housing with the aid of the housing wall and agaseous fluid, in particular a refrigerant, flowing through theopenings.
 21. The refrigeration appliance according to claim 15 whereinbuffer means for storing kinetic energy associated with the motion ofthe compressor piston is provided at each respective reversal point ofthe compressor piston.
 22. A linear compressor particularly suitable andintended for a refrigeration appliance comprising a piston housing; acompressor piston disposed within the piston housing and configured forreciprocatory motion along an axis within the piston housing; and buffermeans for storing kinetic energy associated with the motion of thecompressor piston, wherein the buffer means is configured to store thekinetic energy of the compressor piston in an interim manner bycompression of a gaseous fluid during reciprocatory motion of thecompressor piston.
 23. A method for compressing a gaseous fluid with theaid of a refrigeration appliance comprising the steps of: providing alinear compressor, the linear compressor having a piston housing and acompressor piston configured for recriprocatory movement along an axistherein; providing buffer means for storing kinetic energy associatedwith the motion of the compressor piston, the buffer means including agas cushion; buffering a majority of the kinetic energy of thecompressor piston moving in a recriprocating manner, in particular up tomore than about 90%, using the gas cushion, to cause a reversal of themovement direction of the compressor piston moving in a recriprocatingmanner.
 24. The method according to claim 23 and further comprising thestep of forming the gas cushion using a gaseous fluid sealed using thecompressor piston.
 25. The method according to claim 24 wherein the stepof forming the gas cushion includes using an inner chamber formed by thepiston housing and sealing the compressor piston prior to reversal ofthe piston movement direction, the inner chamber being opened againafter the movement direction of the compressor piston has been reversed.26. The method according to claim 25 wherein the step of forming the gascushion includes sealing the inner chamber within a time interval ofabout ¼ of the period length of the compressor piston reciprocatorymovement, in particular about ⅛ of the period length of the compressorpiston reciprocatory movement, before the time of the movement directionreversal.
 27. The method according to claim 25 wherein the step offorming the gas cushion includes the step of opening the inner chamberwithin a time interval of about ¼ of the period length of the compressorpiston reciprocatory movement, in particular about ⅛ of the periodlength of the compressor piston reciprocatory movement, after the timeof the movement direction reversal.
 28. A method for cooling goodsincluding the steps of providing a refrigeration appliance including alinear compressor, the linear compressor having a piston housing and acompressor piston configured for recriprocatory movement along an axistherein; providing buffer means for storing kinetic energy associatedwith the motion of the compressor piston, the buffer means including agas cushion; buffering a majority of the kinetic energy of thecompressor piston moving in a recriprocating manner, in particular up tomore than about 90%, using the gas cushion, to cause a reversal of themovement direction of the compressor piston moving in a recriprocatingmanner; storing goods for cooling in the refrigeration appliance; andoperating the refrigeration appliance.